The invention relates to an endless vehicular rubber track designed for extreme cold temperature working environment. The invention particularly relates to such track having a combination of tread, supporting carcass and guide lug components of rubber compositions intended for such purpose.
Endless rubber tractor tracks are increasingly being used for propelling various vehicles over the ground such as, for example, various tractors and other agricultural vehicles including, for example, combines and spreaders, as well as various earth moving machines.
Such tracks are conventionally designed for operation over a wide temperature range such as, for example, from xe2x88x9220xc2x0 F. to 70xc2x0 F., (xe2x88x9228xc2x0 C. to 21xc2x0 C.).
However, sometimes it is desired for such tracks to be used under rather extreme cold (e.g. arctic) conditions of temperatures lower than xe2x88x9250xc2x0 F., (xe2x88x9245xc2x0 C.), yet over a wide atmospheric service range of about xe2x88x9255xc2x0 F. to about 90xc2x0 F., (xe2x88x9248xc2x0 C. to about 32xc2x0 C.).
Accordingly, it is desired to provide a vehicular track with components comprised of alternate rubber compositions.
Endless rubber tracks, in general, are conventionally positioned over at least two wheels, normally a drive wheel for engaging an inner surface of the track, often guide lugs as a part of the carcass of the track and driving the track and at least one driven wheel to control the path of the track as it moves to propel the associated vehicle. The outer surface of the peripheral tread component of the track typically contains a plurality of spaced apart raised lugs designed for engaging the ground and assisting the propelling of the associated vehicle such as, for example, a tractor over the ground.
Such tread, in turn, is integral with and supported by a rubber carcass which, for said track, is intended to travel around said drive and driven wheels of an associated vehicle. Rubber guide lugs (which may also serve as drive lugs) are integral with and of a unitary rubber composition with the inner surface of such track carcass.
In practice, the tread of such rubber tracks provide a considerably wider footprint than conventional pneumatic tires and are, thereby, more adaptable to travel over various irregular surfaces such as, in that they offer better flotation over many and varied ground conditions than rubber tires. In addition, use of rubber tracks instead of pneumatic tires may be more useful for traveling over complex ground conditions under relatively extreme cold temperature conditions as compared to vehicles equipped with conventional pneumatic rubber tires.
Historically, the vehicular rubber track carcass component contains continuous steel cables molded into the rubber composition itself to add dimensional stability for the track.
As the rubber track is driven around the aforesaid wheels, it is subject to extensive contortional flexing and, thus, may be subject to tread crack initiation and propagation over time which may be of significant concern when operating the vehicle under very cold conditions.
Accordingly, it is desired that the rubber composition for the tread component and associated carcass and guide lug components of the track have appropriate resistance to flex fatigue, resistance to abrasion and durability under low temperature conditions.
For this description, the term xe2x80x9cphrxe2x80x9d relates to parts by weight of a material or ingredient per 100 parts by weight rubber.
For this description, the terms xe2x80x9celastomerxe2x80x9d and xe2x80x9crubberxe2x80x9d may be used interchangeably unless otherwise indicated, and the terms xe2x80x9ccurexe2x80x9d and xe2x80x9cvulcanizexe2x80x9d may be used interchangeably unless otherwise indicated.
For this description, a glass transition temperature, or Tg, of a material, particularly an elastomer, may be determined by DSC technique, for which ASTM D3418 may be referred to.
In accordance with this invention, an endless rubber track designed to encompass at least one drive wheel and at least one driven wheel wherein said track is comprised of:
(A) an outer rubber tread component comprised of a plurality of spaced apart, raised lugs designed to be ground-contacting,
(B) a unitary
(1) rubber carcass component integral with, underlying and supporting said tread component, and
(2) a guide lug component comprised of a plurality of spaced apart rubber guide lugs positioned on and integral with the outer exposed surface of said carcass component, wherein said guide lugs are and designed to be engaged and/or guided by one or more of said drive and driven wheels, wherein
(a) said tread component is of a rubber composition comprised of, exclusive of elastomers having a Tg higher than xe2x88x9250xc2x0 C. which comprises, based upon 100 parts by weight elastomers (phr),
(1) about 15 to about 40 phr of cis 1,4-polybutadiene elastomer having a Tg within a range of about xe2x88x9290xc2x0 C. to about xe2x88x92115xc2x0 C., and
(2) about 85 to about 60 phr of cis 1,4-polyisoprene rubber having a Tg within a range of about xe2x88x9270xc2x0 C. to about 80xc2x0 C.,
(3) about 38 to about 80 phr of reinforcing filler comprised of about 35 to about 65 phr of rubber reinforcing carbon black and about 3 to about 15 phr of aggregates of precipitated silica, and exclusive of a coupling agent having a moiety reactive with silanol groups on the surface of said silica and another moiety interactive with said elastomer(s),
(4) sulfur curative in a range of about 0.75 to about 1.75 phr and a sulfenamide sulfur cure accelerator,
(5) zero to about 10 phr, and preferably exclusive of, rubber processing oil selected from at least one of aromatic, naphthenic and paraffinic rubber processing oil and their mixtures, and wherein
(b) said unitary carcass and said guide lug components are of a unitary rubber composition, exclusive of elastomers having a Tg higher than xe2x88x9250xc2x0 C., comprised of, based on parts by weight per 100 parts by weight rubber (phr):
(1) about 80 to about 100 phr, alternately about 85 to about 90 phr, of cis 1,4-polyisoprene natural rubber having a Tg within a range of about xe2x88x9270xc2x0 C. to about xe2x88x9280xc2x0 C., and
(2) zero to about 20 phr, alternately about 15 to about 10 phr of synthetic cis 1,4-polyisoprene rubber having a Tg within a range of about xe2x88x9270xc2x0 C. to about xe2x88x9280xc2x0 C.,
(3) about 38 to about 75 phr of reinforcing filler comprised of about 35 to about 60 phr of rubber reinforcing carbon black and about 3 to about 15 phr of aggregates of precipitated silica, and a coupling agent having a moiety reactive with silanol groups on the surface of said silica and another moiety interactive with said elastomer(s),
(4) sulfur curative in a range of about 0.75 to about 1.75 phr and a sulfenamide sulfur cure accelerator
(5) zero to about 10 phr, and preferably exclusive of, rubber processing oil selected from at least one of aromatic, naphthenic and paraffinic rubber processing oil and their mixtures,
(6) about 5 to about 10 phr of rubber plasticizer, other than an oil, and preferably a monomeric, synthetic rubber processor, having a freeze (melt) point (ASTM D1519) of lower than xe2x88x9245xc2x0 C.
A significance of limiting the tread rubber composition of the tread component of said track to the cis 1,4-polybutadiene rubber and cis 1,4-polyisoprene rubber (natural rubber) to the exclusion of other elastomers having a Tg of higher than xe2x88x9250xc2x0 C.
A significance of limiting the unitary carcass component and guide lug component rubber composition the natural cis 1,4-polyisoprene rubber and, optionally said synthetic cis 1,4-polyisoprene rubber to the exclusion of other elastomers having a Tg of higher than xe2x88x9250xc2x0 C. is to promote very low temperature flexibility for the rubber composition.
It is to be appreciated that styrene/butadiene copolymer rubbers (SBR) may often typically have a Tg above xe2x88x9250xc2x0 C., depending somewhat upon whether the SBR is derived from an organic solvent-based polymerization of the styrene and 1,3-butadiene monomers (S-SBR) or an aqueous emulsion polymerization thereof (E-SBR). It is also appreciated that such copolymers may have a Tg lower than xe2x88x9250xc2x0 C. if such copolymer has very low styrene content. Therefore, a minor amount (e.g. not more than about 15 phr) of such copolymer having a Tg below xe2x88x9250xc2x0 C. might be included in either said track tread rubber composition or in said track unitary carcass and guide lug rubber composition, although, in general, is preferred that said track tread rubber composition and said track carcass/guide lug rubber compositions are exclusive of a styrene/butadiene copolymer rubber.
Preferably the carbon black for said tread, carcass and guide lug components is characterized by having an Iodine Number in a range of about 115 to about 130 g/kg, a DBP value in a range of about 105 to about 125 cm3/100 g, and a Tint value in a range of about 120 to about 140 in order to promote acceptable abrasion resistance for the rubber composition.
One or more low freeze (melt) point rubber plasticizers are used for said unitary carcass and guide lug component rubber composition in order to promote a very low temperature durability for the tread carcass rubber composition.
Representative of such synthetic, non-oil, monomeric, rubber plasticizers, for example, are low freeze (melt) point rubber plasticizers (compatible with diene-based elastomers) having a freeze (melt) point of lower than xe2x88x9245xc2x0 C. Many plasticizers for rubber compositions are known to those having skill in such art who would also be aware that some of such plasticizers have such low freeze (melt) points.
Representative examples of such plasticizers intended for use in various rubber compositions having a freeze (melt) point within a range of xe2x88x9245xc2x0 C. to about xe2x88x9265xc2x0 C. or lower, although not intended herein to be limiting are, for example, one or more of adipates, azelates, gluterates, sebacates, oleates, hexoates, tallates and trimellitates.
Representative examples of such adipates are, for example, alkyl alkyldiester adipate as Plasthall(copyright) 7006, diioctyl adipate as Plasthall DIOA, dioctyl adipate as Plasthall DOA, polyester adipate as Plasthall P-634, diisooctyl adipate as Monoplex DDA and dioctyl adipate as Monoplex DOA, all from the CP Hall Company.
Representative examples of such azelates is, for example, dioctyl azelate as Plastall DOZ from the CP Hall Company.
Representative of such gluterates are, for example, dialkyl diether gluterate as Plasthall 7050, dibutoxyethoxyethyl gluteratate as Plasthall 224, dibutoxyethyl glutarate, and diisodecyl glutarate as Plasthall 201, all from the CP Hall Company.
Representative of such oleates are, for example, alkyl oleate as Plasthall 7049 and butyl oleate as Plasthall 503, all from the CP Hall Company.
Representative of such sebacates are, for example, dioctyl sebacate as Plasthall DOS, all from the CP Hall Company.
Representative of a tallate is, for example, isooctyl tallate as Plasthall 100 from the CP Hall Company.
Representative of trimellitates are, for example, triisooctyl trimellitate as Plasthall TIOTM, trioctyl trimellitate as Plasthall TOTM and linear trimellitate as: Plasthall LTM, all from the CP Hall Company.
Representative of hexoates are, for example, polyethylene glycol 400 di-2-ethylhexoate as TegMer(copyright) 809, tetraethylene glycol di-2-ethylhexoate as TegMeR(copyright) 804, and tetraethylene glycol di-2-ethyhlhexoate as TegMer(copyright) 804 special, all from the CP Hall Company.
Representative of another rubber plasticizer is diisooctyl dodecanedioate as Plasthall DIODD from the CP Hall Company.
In further accordance with this invention, a vehicle is provided having at least two endless rubber track systems, namely a track system on each side of the vehicle, for driving said vehicle over the ground, said track systems individually comprised of the track of this invention, a plurality of wheels engaged with said vehicle and encompassed by said track wherein at least one of said wheels is a drive wheel.
The flex fatigue limitation of the cured track""s tread rubber composition is considered herein to be important or significant to the durability and service life of the track tread.
The abrasion resistance of the cured track""s tread rubber composition is considered herein to be important or significant to wear performance of the track tread (e.g.: resistance to wear due to abrasion).
The prescribed combination of elastomers, carbon black, silica and antioxidant content of the cured track""s tread rubber composition is considered herein to be important or significant to aid in achieving the track tread""s performance (e.g.: resistance to flex fatigue and resistance to wear).
Significant aspects of this invention include:
(A) use of a combination of natural rubber and cis 1,4-polybutadiene rubber for the track tread designed to promote treadwear and flex fatigue resistance,
(B) relatively low level (content) of sulfur curative designed to promote less crosslinking and higher chain extension of the tread rubber composition,
(C) exclusion of a coupling agent for the silica for the track tread designed to increase the cured elastomer composition""s resistance to flex fatigue and maintain resistance to tear propagation as compared to such composition using a silica coupling agent,
(D) specified carbon black as a tire tread grade of carbon black for the track tread in order to promote suitable tear strength and resistance or tread service related damage
(E) relatively low level of rubber processing oil, if any.
Indeed, while the individual ingredients are known, it is considered that the above combination of ingredients for the tread component of the endless track for this invention is novel and inventive.
Significant aspects for the unitary rubber carcass component and said guide lug component rubber compositions are:
(A) use of cis 1,4-polyisoprene natural rubber and, optionally synthetic cis 1,4-polyisoprene rubber designed to promote flex fatigue resistance,
(B) relatively low level (content) of sulfur curative designed to promote less crosslinking and higher chain extension of the tread rubber composition,
(C) inclusion of a of a coupling agent for the aggregates of silica designed to enhance tear strength of the rubber composition and adhesion to other rubber components of the track.
(D) specified carbon black as a tire grade of carbon black intended to promote an acceptable tear strength and resistance to abrasion for the rubber composition.
(E) relatively low level of rubber processing oil, if any.
(F) use of a low freeze (melt) point plasticizer, other than oil and preferably a monomeric, synthetic rubber plasticizer, in order to promote very low temperature durability and resistance to flex fatigue for the rubber composition.
The track, including its tread component, is then sulfur cured (vulcanized) in a suitable mold at an elevated temperature (e.g.: about 150xc2x0 C. to about 170xc2x0 C.).
Accordingly, the invention also contemplates a sulfur-vulcanized endless track. Further, the invention contemplates a vehicle having at least two endless rubber track systems (each on an opposite side of the vehicle) for driving said vehicle over the ground, said track systems individually comprised of said track, a plurality of wheels engaged with said vehicle and encompassed by said track wherein at least one of said wheels is a drive wheel.